Additional Tutorial Notes:
When working with lights be sure to change the composition to Adaptive Resolution instead of OpenGL. You may also try using a Spot Light instead of a Point Light.

First import your footage. Create a new Comp and add a Camera.
Make a new white solid as a ground floor, set it as 3D, rotate it on x-axis to 90° and adjust the camera that the solid matches your footage.
You could also apply a grid on the solid to have more control in adjusting the camera.
Create a new text, set it as 3D. Position it vertically right on the floor and in the "Material Options" set the "Cast Shadows" to "On".
Add a new Point-light with the checkbox for "Cast Shadows" activated and the color that fits best to your footage. Position it in the 3D-Space for your needs.
Deactivate the grid of your floor and set it's blending mode to "Multiply" and in the "Material Options" set the "Accepts Lights" to "Off"
Select the created light and in the "Light Options" increase the "Shadow-Diffusion" as you like to blur the shadow.
In the "Material Options" of your Text-Layer you can also set "Accepts Lights" to "Off" and recolor your text as you like.

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Advanced Extrusion with Shatter

This is a fairly simple technique often done poorly. The trick to making the 3D extrusion look as good as possible is in the way you use a custom shape layer and the way you assign textures to the extrusion.